Archives of Toxicology

The management of N-nitrosamine impurities challenges pharmaceutical development and regulation worldwide. Because most medicinal exposures are shorter than lifetime and absolute impurity exclusion is impossible, reliable approaches to define duration-specific intake limits are essential. On the premise that carcinogenic risk is proportional to cumulative dose, the Less-Than-Lifetime (LTL) Threshold of Toxicological Concern (TTC) framework defines progressively lower intake limits for mutagenic impurities over longer exposures. However, N-nitrosamines are currently treated as a cohort of concern, necessitating compound-specific evaluation placing reliance on in vivo mutagenicity assays for impurity qualifications. To better understand durational potency relationships and the application domain of the LTL-TTC, we apply benchmark dose (BMD) modelling to cumulative-dose-scaled transgenic rodent (TGR), error-corrected sequencing and rodent carcinogenicity datasets for N-nitrosodimethylamine (NDMA) obtained from the published literature. For TGR, cumulative-dose scaling better resolved liver as the most sensitive organ and reduced interstudy variability: liver BMDs spanned [~]80-fold in daily-dose units but only [~]20-fold when scaled to cumulative dose. Among closely-matched mouse liver gavage studies, cumulative-dose BMDs only varied by [~]2.5-fold across 1 to 28-day treatment regimens. Error-corrected sequencing also demonstrated parity, with acute-dose regimens producing mutation burdens near-identical (< 1.2-fold) to those cumulated from 28-day repeat-dose regimens. Comparable results were obtained from carcinogenicity datasets confirming proportionality-of-effect to cumulative dose. These findings empirically support the validity of the LTL-TTC concept. More broadly, they demonstrate that short-term in vivo mutagenicity assays can serve as reliable surrogates for lifetime carcinogenicity studies, strengthening the scientific and regulatory basis for duration-adjusted acceptable intakes for N-nitrosamine impurities.

High-throughput physiologically based kinetic (HT-PBK) modelling provides a mechanistic framework for predicting systemic pharmacokinetics (PK) from in vitro and in silico data, supporting non-animal chemical safety assessment within Next generation risk assessment (NGRA). Here, we applied HT-PBK modelling to dermal exposure, a key route of human contact with chemicals. Using the skin permeation model of the Open Systems Pharmacology Suite, we simulated systemic PK profiles of 52 compounds based solely on physicochemical properties predicted by quantitative structure-activity relationship (QSAR) models and without any compound-specific in vitro measurements. We systematically compared different QSAR tools for lipophilicity, solubility, and other parameters to identify optimal model parameterisation strategies. Across all compounds, the best-performing HT-PBK strategy predicted 75% of Cmax and AUC values within a tenfold range of observed human plasma data extracted from published clinical studies. A systematic tendency toward overprediction of systemic PK was observed, likely due to missing study metadata and the default assumption of fully hydrated skin. Prediction errors were larger for dermal than for oral exposure, reflecting the greater complexity and variability of dermal absorption processes. Nevertheless, key exposure metrics were reproduced within acceptable limits. These results demonstrate the feasibility of fully in silico, non-animal HT-PBK modelling for dermal absorption and support its use as a pragmatic tool for exposure-driven safety assessment within NGRA frameworks.

Background & AimsOne of the early key events of drug-induced liver injury (DILI) is the activation of adaptive stress responses, a cellular mechanism to overcome stress. Given the diversity of DILI outcomes and lack in understanding of population variability, we mapped the inter-individual variability in stress response activation to improve DILI prediction. Approach & ResultsHigh-throughput transcriptome analysis of over 8,000 samples was performed in primary human hepatocytes of 50 individuals upon 8 to 24 h exposure to broad concentration ranges of stress inducers: tunicamycin to induce the unfolded protein response (UPR), diethyl maleate for the oxidative stress response, cisplatin for the DNA damage response and TNF for NF-{kappa}B signalling. This allowed investigation of the inter-individual variability in concentration-dependent stress response activation, where the average of benchmark concentrations (BMCs) had a maximum difference of 864, 13, 13 and 259-fold between different hepatocytes for UPR, oxidative stress, DNA damage and NF-{kappa}B signalling-related genes, respectively. Hepatocytes from patients with liver disease resulted in less stress response activation. Using a population mixed-effect framework, the distribution of BMCs and maximum fold change were modelled, allowing simulation of smaller or larger PHH panel sizes. Small panel sizes systematically under-estimated the variance and resulted in low probabilities in estimating the correct variance for the human population. Moreover, estimated toxicodynamic variability factors were up to 2-fold higher than the standard uncertainty factor of 101/2 to account for population variability during risk assessment, exemplifying the need of data-driven variability factors. ConclusionsOverall, by combining high-throughput transcriptome analysis and population modelling, improved understanding of variability in stress response activation across the human population could be established, thereby contributing towards improved prediction of DILI.

The foodborne mycotoxins alternariol (AOH) and alternariol monomethyl ether (AME) have been associated with several adverse effects, including cytotoxicity, genotoxicity, endocrine disruption, and immunomodulation. As these endpoints are typically observed in vitro at micromolar concentrations, the question arises whether such levels are attainable in exposed humans. To address this data gap in chemical risk assessment, a physiologically based kinetic (PBK) model was developed to predict internal exposure doses to AOH and AME in humans. As input parameters, kinetic constants for hepatic glucuronidation were obtained in vitro by incubating Sprague Dawley rat and human liver S9 fractions with 0.5-50 M AOH and 0.5-20 M AME, demonstrating rapid biotransformation in both species. Intestinal absorption of AME and physicochemical parameters were estimated using quantitative structure-activity relationship (QSAR) models. Sensitivity analysis identified parameters describing hepatic glucuronidation and gastrointestinal uptake as among the most influential, confirming the importance of their reliable estimation. The PBK model was evaluated against available rodent toxicokinetic data and subsequently extrapolated to humans. Ultimately, the currently available exposure estimates published by EFSA in 2016 were applied to predict target tissue concentrations, which were compared to points of departure (PoDs) for relevant toxicological endpoints. Even in the most susceptible group of male toddlers, predicted internal concentrations (10-4 M range) were approximately four orders of magnitude below the respective PoDs. Consequently, under the applied exposure assumptions and considering the compounds as isolated chemicals, AOH and AME are not expected to reach systemic or tissue concentrations associated with the investigated effects.

The presence of N-nitrosamine drug substance-related impurities (NDSRIs) in pharmaceuticals represents a significant regulatory and safety challenge due to their classification as "cohort of concern" compounds. This paper describes the toxicological evaluation of N-Nitrosotrimetazidine (NTMZ), performed to refine the initial default acceptable intake (AI) limits of 18 to 26.5 ng/day established by regulatory authorities. The evaluation followed a tiered approach: NTMZ was first confirmed as mutagenic in vitro via the standard Ames test. To further investigate its genotoxic potential, two in vivo studies were conducted in Wistar and transgenic rats. Detection of DNA strand breaks in the liver and duodenum (comet assay) together with positive results in the cII mutation assay confirmed an in vivo mutagenic mode of action. Benchmark Dose (BMD) analysis of the transgenic rat data yielded a BMDL50 of 7 mg/kg/day in the male liver. To characterize long-term carcinogenic risk, a GLP-compliant 2-year carcinogenicity study was conducted in Wistar rats. Chronic exposure induced dose-dependent increases in liver tumors (hemangiosarcomas, hepatocellular carcinomas and adenomas) and intestinal tumors (adenomas and adenocarcinomas), leading to a Tumor Dose 50 (TD50) of 23 mg/kg/day in male rats. Benchmark dose analysis of tumor incidence identified a lowest BMDL10 of 2.6 mg/kg/day in females, which served as the basis for deriving an AI of 13 microg/day. This assessment demonstrates a strong predictive correlation between the BMD derived from the in vivo transgenic model, the BMDL10 and the final TD50 values obtained in the 2-year carcinogenicity study. These findings provided the scientific basis for establishing a conservative AI of 13 microg/person/day based on the BMDL10 and further support the regulatory acceptance and use of BMD-derived approaches for the evaluation of nitrosamine impurities.

Abstract Background. Acrylamide, a neurotoxicant in heated foods and smoke, is linked to occupational neuropathy, but evidence regarding chronic, low-level population exposure remains limited. We evaluated the association between acrylamide exposure biomarkers and peripheral neuropathy among U.S. adults. Methods. A total of 2,266 NHANES 2003-2004 participants (age >40) were analyzed. Exposure was assessed via hemoglobin adducts (HbAA/HbGA); neuropathy via monofilament testing >1 site). Survey-weighted logistic regression models adjusted for confounders. Sensitivity analyses included cubic splines, diabetes stratification, and multiple imputation. Results. Neuropathy prevalence was 15.5%. In adjusted models, neither adduct was associated with neuropathy (HbAA OR: 0.98, 95% CI: 0.82-1.17; HbGA OR: 0.91, 95% CI: 0.77-1.08). No dose-response gradient was observed. Expected risk factors (age, diabetes) showed strong associations, validating model sensitivity. The null result remained robust across sensitivity analyses, including a stricter outcome definition and multiple imputation (pooled OR: 0.97, 95% CI: 0.83-1.14). Conclusions. Acrylamide adducts were not associated with peripheral neuropathy in this national sample. General population levels (~55-70 pmol/g) lie well below established occupational no-observed-adverse-effect levels (~510 pmol/g) and clinical neuropathy thresholds (~6,000 pmol/g), providing a mechanistically coherent explanation for this null result.

Integrating high-throughput in vitro data into next-generation risk assessment (NGRA) workflows requires screening strategies that yield quantitative potency estimates and mechanistically interpretable biological signals. Transcriptomic and morphological profiling are increasingly adopted for early-stage hazard identification by enabling triage of substances for resource-intensive follow-up and prioritizing candidates most likely to present meaningful risk. In this study, we aimed to characterize biological concordance and uncertainty by quantifying how well high-throughput transcriptomics (HTTr) and Cell Painting PLUS (CPP) bioactivity profiles recover target-relevant biological signals in immortalized human renal proximal tubule epithelial RPTEC/TERT1 cells using 313 reference chemicals with high-confidence target annotations. Through quality control procedures and biological activity filters we yielded 142 reference chemicals spanning 66 different targets, which were systematically evaluated for biological concentration-responses by HTTr and CPP. HTTr was evaluated using TXG-MAPr-based qualitative and quantitative gene network activity analysis. HTTr showed the most prominent activity for targets that were highest expressed in RPTEC/TERT1 cells. Active chemical-pairs showed strong gene network activity correlation albeit with different potencies. Similarly, the highest transcriptomic concordance was observed for reference chemicals acting in the same pathway, such as EGFR/MEK or PI3K/AKT/mTOR. CPP often showed high sensitivity primarily at the organelle level providing limited statistical power for chemical grouping. Collectively, the results support HTTr and CPP as complementary early-tier assays within an in vitro weight-of-evidence safety testing framework. Although CPP is suitable as a cost-effective screening modality, HTTr offers higher mechanistic resolution for mode-of-action inference in high-throughput bioactivity screening and therefore remains necessary for high-confidence mechanistic interpretation.

Per- and poly-fluoroalkyl substances (PFAS) are widely found in the environment because of their extensive use and persistence. Although several PFAS are well studied, most lack toxicity data to inform human health hazard and risk assessment. This study focussed on four model PFAS: perfluorooctanoic acid (PFOA; 8 carbon), perfluorobutane sulfonate (PFBS; 4 carbon), perfluorooctane sulfonate (PFOS; 8 carbon), and perfluorodecane sulfonate (PFDS; 10 carbon). Human primary liver cell spheroids (pooled from 10 donors) were exposed to 10 concentrations of each PFAS and analyzed at four time-points. The approach aimed to: (1) identify gene expression changes mediated by the PFAS; (2) identify similarities in biological responses; (3) compare PFAS potency through benchmark concentration analysis; and (4) derive bioactivity exposure ratios (ratio of the concentration at which biological responses occur, relative to daily human exposure). All PFAS induced transcriptional changes in cholesterol biosynthesis and lipid metabolism pathways, and predicted PPAR activation. PFOS exhibited the most transcriptional activity and had a highly similar gene expression profile to PFDS. PFBS induced the least transcriptional changes and the highest benchmark concentration (i.e., was the least potent). The data indicate that these PFAS may have common molecular targets and toxicities, but that PFOS and PFDS are the most similar. The transcriptomic bioactivity exposure ratios derived here for PFOA and PFOS were comparable to those derived using rodent apical endpoints in risk assessments. These data provide a baseline level of toxicity for comparison with other known PFAS using this testing strategy.

An important element of the European Unions "Registration, Evaluation, Authorisation and Restriction of Chemicals" (REACH) regulation is the evaluation by the European Chemicals Agency (ECHA) of testing proposals submitted by the registrants to address data gaps in standard REACH information requirements. The registrants may propose adaptations, and ECHA evaluates the reasoning and issues a written decision. Read-across is a common adaptation type, yet it is widely assumed that ECHA often does not agree that the justifications are adequate to waive standard testing requirements. From 2008 to August 2023, a total of 2,630 Testing Proposals were submitted to ECHA; of these, 1,538 had published decisions that were systematically evaluated in this study. Each document was manually reviewed, and information extracted for further analyses. Read-across hypotheses were standardized into 17 assessment elements (AEs); each submission was classified as to the AEs relied upon by the registrants and by ECHA. Data was analyzed for patterns and associations. Testing Proposal Evaluations (TPEs) with adaptations comprised 23% (353) of the total; analogue (168) or group (136) read-across adaptations were most common. Of 304 read-across-containing TPEs, 49% were accepted; the odds of acceptance were significantly greater for group read-across submissions. The data was analyzed by Annex (i.e., tonnage), test guideline study, read-across hypothesis AEs, as well as target and source substance types and their structural similarity. While most ECHA decisions with both positive and negative decisions on whether the proposed read-across was adequate were context-specific, a number of significant associations were identified that influence the odds of acceptance. Overall, this analysis provides an unbiased overview of 15 years of experience with testing proposal-specific read-across adaptations by both registrants and ECHA. These data will inform future submissions as they identify most critical AEs to increase the odds of read-across acceptance.

The ubiquitously occurring food contaminants altenuene (ALT) and tentoxin (TEN) are recognized as emerging Alternaria mycotoxins, yet substantial data gaps remain when it comes to their toxicological behavior and toxicokinetic characteristics. This study aimed to compare and generate quantitative data on their hepatic metabolism and to obtain semi-quantitative insights into their metabolite profiles. To this end, primary rat and human hepatocytes were incubated with 10 {micro}M ALT or TEN over multiple time points up to 4 h. Both substrate depletion and metabolite identification revealed pronounced interspecies differences. The extent of ALT metabolism was significant, with an 88% and 57% decrease in rat and human hepatocytes after 4 h, respectively. In contrast, TEN showed extensive biotransformation in rats (67%) but only modest turnover in humans (27%) over the same period. Hepatocellular clearances were consistently higher for ALT than TEN, with hepatic extraction ratios indicating intermediate extraction for ALT and low extraction for TEN. High-resolution mass spectrometry combined with targeted analysis of selected metabolites annotated phase II conjugation as the predominant metabolic pathway for ALT and phase I oxidative metabolism for TEN, including mono- and double-metabolized species for the latter. Overall, these results provide a comprehensive characterization of ALT- and TEN-metabolism in hepatocytes, offering a foundation for future studies on their toxicological relevance and impact on human health.

The transition toward animal-free safety assessment of chemicals has accelerated the development of New Approach Methodologies (NAMs) for predicting skin sensitization. However, individual in silico models and experimental NAM assays frequently produce inconsistent or contradictory results, limiting their reliability when used in isolation. To address this challenge, we present a tiered integrated assessment framework implemented through the open source SaferSkin application, which enables systematic comparison and integration of multiple predictive models and experimental data within a transparent weight-of-evidence workflow. In this case study, a diverse set of 21 reference compounds was evaluated using a battery of in silico approaches, including the OECD QSAR Toolbox, VEGA, CASE Ultra and additional machine-learning models implemented within SaferSkin. The platform enables side-by-side comparison of predictions and integration of experimental data through Bayesian network models, allowing probabilistic updating of predictions as new evidence becomes available. Our results demonstrate that reliance on any single predictive model is insufficient for robust hazard identification due to frequent disagreement between models. In contrast, consensus interpretation across multiple modelling approaches combined with targeted experimental evidence substantially improves predictive confidence. The integrated weight-of-evidence framework showed strong concordance with reference classifications and was further supported by independent validation using the Pred-Skin Bayesian model. Importantly, the tiered workflow enables resolution of ambiguous cases. For example, lower-tier predictions for ethyl (2E,4Z)-deca-dienoate were inconsistent across models, whereas targeted third-tier testing using the SENS-IS assay identified the compound as a strong sensitiser (GHS Category 1A). Overall, this study demonstrates how integrated modelling, Bayesian evidence updating and targeted NAM testing can reduce uncertainty in skin sensitization assessment. The SaferSkin framework provides a transparent and reproducible approach for implementing Next Generation Risk Assessment (NGRA) strategies and supports the development of animal-free regulatory toxicology and Safe-and-Sustainable-by-Design chemical innovation. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/711911v1_ufig1.gif" ALT="Figure 1"> View larger version (45K): org.highwire.dtl.DTLVardef@b59ca0org.highwire.dtl.DTLVardef@13de455org.highwire.dtl.DTLVardef@599358org.highwire.dtl.DTLVardef@d87fd1_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical AbstractC_FLOATNO C_FIG

Per- and polyfluoroalkyl substances (PFAS) are some of the most prominent organic contaminants in human blood. Although the toxicological implications from human exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) are well established, data on lesser-understood PFAS are limited. New approach methodologies (NAMs) that apply bioinformatic tools to high-throughput data are being increasingly considered to inform risk assessment for data-poor chemicals. The aim of this investigation was to identify biological response potencies (i.e., benchmark concentrations: BMCs) following PFAS exposures to inform read-across for risk assessment of data-poor PFAS. Gene expression changes were measured in primary human liver cell microtissues (i.e., 3D spheroids) after 1-day and 10-day exposures to increasing concentrations of 23 PFAS. The cells were treated with four subgroups of PFAS: carboxylates (PFCAs), sulfonates (PFSAs), fluorotelomers, and sulfonamides. An established pipeline to identify differentially expressed genes and transcriptomic BMCs was applied. We found that both PFCAs and PFSAs exhibited a trend toward increased transcriptional changes with carbon chain-length. Specifically, longer-chain compounds (7 to 10 carbons) were more likely to induce changes in gene expression, and have lower transcriptional BMCs. The combined high-throughput transcriptomic and bioinformatic analyses supports the capability of NAMs to efficiently assess the effects of PFAS in liver microtissues. The data enable potency ranking of PFAS for human liver cell spheroid cytotoxicity and transcriptional changes, and assessment of in vitro transcriptomic points of departure. These data improve our understanding of the health effects of PFAS and will be used to inform read-across for human health risk assessment.

Error-corrected Duplex Sequencing (DuplexSeq) enables direct quantification of low-frequency mutations and offers tremendous potential for chemical mutagenicity assessment. We investigated the utility of DuplexSeq to quantify induced mutation frequency (MF) and spectrum in human lymphoblastoid TK6 cells exposed to a prototypical DNA alkylating agent, N-ethyl-N-nitrosourea (ENU). Furthermore, we explored appropriate experimental parameters for this application, and assessed inter-laboratory reproducibility. In two independent experiments in two laboratories, TK6 cells were exposed to ENU (25-200 {micro}M) and DNA was sequenced 48, 72, and 96 h post-exposure. A DuplexSeq mutagenicity panel targeting twenty 2.4-kb regions distributed across the genome was used to sample diverse, genome-representative sequence contexts. A robust increase in MF that was unaffected by time was observed in both laboratories. Concentration-response in the MF from the two laboratories was strongly positively correlated (R2=0.95). C:G>T:A, T:A>C:G, T:A>A:T, and T:A>G:C mutations increased in consistent, concentration-dependent manners in both laboratories, with high proportions of C:G>T:A at all time points. The target sites responded similarly between the two laboratories and revealed a higher average MF in intergenic regions. These results, demonstrating remarkable reproducibility across time and laboratory for both MF and spectrum, support the high value of DuplexSeq for characterizing chemical mutagenicity in both research and regulatory evaluation.

Cytochrome P450 (CYP)-mediated biotransformation of endogenous and xenobiotic substances can lead to altered exposure, toxicological impact, or adverse drug reactions. CYP induction data are fundamental to regulatory chemical toxicity hazard assessment because they directly affect the in vivo fate of xenobiotics, potentially influencing their safety and efficacy of pharmaceuticals, and impacting the safety assessment of industrial chemicals, and environmental contaminants. Here we report on the third laboratory supplementary validation of an established and previously validated human HepaRGTM in vitro method able to detect CYP1A2, CYP2B6, and CYP3A4 induction, to support the expansion of the chemical applicability domain beyond pharmaceuticals. This study was conducted to support the part 1 study with additional robust data. We established the test method in-house using the 10 previously validated pharmaceutical proficiency chemicals, then tested a further 6 proposed augmentation chemicals, tebuconazole, benfuracarb, chlorpyrifos, N, N-Diethyl-meta-toluamide, fipronil, permethrin, as tested in part 1, and then four additional chemicals: prochloraz, atrazine, pyrimethanil, and chlorpyrifos-methyl. LC-MS/MS was utilised to measure the conversion of a cocktail mixture of prototypical selective CYP probe substrates to their metabolites, in parallel with mRNA measurements. We achieved high concordance with expected classifications for proficiency and additional chemicals. Comparisons with mRNA-based measurements suggested gene expression may serve as a cost-effective pre-screening tool for CYP1A2 and CYP3A4, though with greater uncertainty for CYP2B6. The data support the robustness of the HepaRG method for CYP induction testing and the adoption of the test method in 2026 as an Organisation for Economic Cooperation and Development Test Guideline. Plain language summaryCytochrome P450 (CYP) enzymes metabolize drugs, pesticides, and other chemicals. Chemicals that increase or decrease CYP enzyme activity can change internal exposure levels, potentially leading to unexpected toxicity or impact drug effectiveness. Reliable in vitro methods to assess CYP induction are needed for regulatory chemical safety assessment. This study describes results from a third laboratory applying a previously validated human HepaRG cell-based method to assess induction of CYP1A2, CYP2B6, and CYP3A4. After successful in-house implementation using ten reference pharmaceutical compounds, the method was extended to ten more industrial chemicals. CYP induction was evaluated by measuring enzyme activity and changes in gene expression. The test method showed a high level of agreement with expected induction outcomes. Gene expression data supported enzyme activity results, particularly for CYP1A2 and CYP3A4. These results strengthen confidence in the robustness and wider applicability of the method for Organisation for Economic Cooperation and Development Test Guideline adoption.

We have previously shown that the thyroid hormones triiodothyronine (T3) and thyroxine (T4) prolong anagen, mitigate stem cell apoptosis, and stimulate mitochondrial functions in microdissected human scalp HFs ex vivo. To circumvent the systemic adverse effects of T3/T4, we have asked in the current pilot study whether topically applied T3/T4 retains hair growth-promoting properties. To prove this, we have topically treated healthy full-thickness human scalp skin with T3 (1, 10nM) and T4 (1, 10M) for six days in serum-free organ culture, using an HF-targeting vehicle that contains only FDA-approved ingredients. This showed that, at distinct doses, topical T3 and T4 significantly increased the percentage of HFs in anagen, decreased the percentage of proliferative (Ki-67+) cells in the hair matrix, did not promote melanogenesis (as measured by quantitative Warthin-Starry histochemistry), and significantly increased keratin 15 expression in the bulge. Finally, T3 and T4, at low concentrations, increase the expression of the hair growth promoters IGF-1 and FGF-7. The lower concentration of T3 and both of T4 also significantly increases the number of CD31+ endothelial cells, suggesting a pro-angiogenic effect, which is also important for hair growth promotion. These preliminary results strongly suggest that topically applied thyroid hormones promote hair growth in intact human scalp on multiple levels ex vivo. This invites the intermittent pulse application of topical T3 and T4 as a novel therapeutic intervention for managing hair loss disorders associated with telogen effluvium, such as androgenetic alopecia.

Cytochrome P450 (CYP) enzymes play a key role in the metabolism of both xenobiotics and endogenous compounds, and the activity of some CYP isoforms are susceptible to induction and/or inhibition by certain chemicals. As CYP induction and inhibition can significantly alter the in vivo fate of xenobiotics i.e., levels of parent chemicals and/or metabolites, and thus toxicity, CYP induction/inhibition data is needed for regulatory chemical toxicity hazard assessment. Utilizing available human in vivo pharmaceutical data, a successful validation was previously conducted on the in vitro HepaRG CYP induction test method for measurement of induction of three key human CYP enzymes CYP1A1/1A2, 2B6 and 3A4. However, further validation data was required to demonstrate applicability of the test method to also accurately detect CYP induction mediated by industrial and pesticidal chemicals. Here we report on the supplementary validation of the HepaRG CYP enzyme induction test method carried out in two laboratories under the auspices of the EU Horizon2020-funded project "GOLIATH", to expand the chemical applicability domain beyond pharmaceutical chemicals. Successful transfer was demonstrated and reproducibility assessed for the original 10 selected proficiency pharmaceuticals, plus three reference inducers together with six additional non-pharmaceutical augmentation chemicals. The method and chemical selection were found to be reliable and relevant for the routine assessment of human CYP induction. For the augmentation chemicals being proposed as additional proficiency chemicals, the test method achieved a reasonable but not optimum reproducibility. Recommendations are proposed to improve the test methods specificity, reflecting the inherent uncertainty around borderline CYP inducing chemicals. Plain language summaryCytochrome P450 (CYP) enzymes help break down drugs and other chemicals in the body. Their activity can be increased (induced) or decreased (inhibited), which can change how toxic a chemical is and when it is excreted. Because of this, CYP data is important for chemical safety assessments. A laboratory-based method using HepaRG cells was previously validated to measure induction of key CYP enzymes (CYP1A1/1A2, CYP2B6 and CYP3A4) using pharmaceutical chemicals. This study aimed to show that it also works well for industrial and pesticidal chemicals. In the EU funded GOLIATH project, two laboratories tested 10 pharmaceutical and 6 non-pharmaceutical chemicals. The method showed good reliability overall and strong reproducibility for pharmaceuticals. For non-pharmaceutical chemicals, results were acceptable but less consistent. The study concludes that the method is useful for routine testing, but improvements are needed to increase accuracy and better handle chemicals that show weak or borderline CYP induction effects.

Adverse outcome pathways (AOPs) describe stressor non-specific sequences of events between a first molecular trigger (molecular initiating event, MIE), causally linked key events (KEs), and an adverse outcome (AO). AOPs are intended to aid in chemical toxicity testing as a new approach methodology. However, commonly used AOP development methods depend on manual curation, which is labor intensive. As a result, there are still relatively few AOPs and a huge number of toxicity mechanisms and possible adverse outcomes remain undescribed. Therefore, systematic and high-throughput approaches to predict new AOPs are needed. Here, we developed and implemented a data integration-based framework to generate new candidate AOPs using insecticides and Parkinson Disease as a proof of concept. We integrated and statistically linked disconnected databases (e.g., Comparative Toxicogenomics Database, Human Protein Atlas, and Gene Ontology) to form MIE - KE (cell level) - KE (tissue level) - AO candidate AOPs. Through this systematic process, we generated 562,117 candidate AOPs, which we then scored using a weight of evidence (WoE) approach and prioritized 12,756 AOPs with a WoE >0.5. Through random sampling of 100 prioritized AOPs, we found 70% had external literature supporting their biological plausibility, and only 15% represented identifiably implausible associations. The prioritized AOPs describe varied mechanisms of toxicity related to e.g., MAPK, PTEN, and FGFR signaling pathways, with "increases phosphorylation of MAPK1" as the most frequent MIE. Our AOP generating approach yields consistently structured AOPs and can complement existing and emerging development methods to expand AOP coverage across different stressors and outcomes.

Inter-individual and population variability in susceptibility to chemical exposures confounds determination of threshold exposure levels to protect the most vulnerable. Current risk assessment frameworks, in the absence of empiric chemical-specific data, generally recommend default or probabilistic adjustment factors to account for such variability. We present an experimental approach to incorporate common genetic variants potentially impacting population-level differences in toxicant susceptibility into human cell-based models for any cellular apical endpoint of interest. We focus on the genes with the most common aggregate loss-of-function (LoF) alleles in the gnomAD v3.0 data which we designated as the PopVarLoF set. Unexpectedly, enrichment analysis of these genes found significant overrepresentation of gene products playing important functional roles in toxicology. Interrogation of GWAS and PheWAS databases found that these genes are associated with diverse metabolic phenotypes consistent with the relevance of the PopVarLoF set in studying variability of toxicant response in human populations. We further characterized the PopVarLoF set by developing custom lentiviral CRISPR knockout libraries targeting the PopVarLoF genes to assess their functional essentiality in the HepG2/C3A cell line. Functional disruption of 14 of the PopVarLoF genes ([~]1 %) without toxicant exposure resulted in significant growth defects in this cell line, consistent with the majority of PopVarLoF gene products having non-essential roles. The development of human cell-based toxicity assays or other NAMs which include the empiric assessment of common genetic sources of population variability in susceptibility to chemical exposure could contribute to more robust risk assessment which protects vulnerable populations while reducing uncertainty. Impact statementWe characterize common loss of function genetic variants which could impact toxicant susceptibility and describe an approach to incorporate them into NAMs to enable empiric estimates of the contribution of genetic variability to diverse toxicity endpoints.

Organophosphorus pesticides (OPs) are a chemically diverse class of commonly used insecticides. Epidemiological studies suggest that low dose chronic prenatal and infant exposures can lead to life-long neurological damage and behavioral disorders. While inhibition of acetylcholinesterase (AChE) is the shared mechanism of acute OP neurotoxicity, OP-induced developmental neurotoxicity (DNT) can occur independently and/or in the absence of significant AChE inhibition, implying that OPs affect alternative targets. Moreover, different OPs can cause different adverse outcomes, suggesting that different OPs act through different mechanisms. These findings emphasize the importance of comparative studies of OP toxicity. Freshwater planarians are an invertebrate system that uniquely allows for automated, rapid and inexpensive testing of adult and developing organisms in parallel to differentiate neurotoxicity from DNT. Effects found only in regenerating planarians would be indicative of DNT, whereas shared effects may represent neurotoxicity. We leverage this unique feature of planarians to investigate potential differential effects of OPs on the adult and developing brain by performing a comparative screen to test 7 OPs (acephate, chlorpyrifos, dichlorvos, diazinon, malathion, parathion and profenofos) across 10 concentrations in quarter-log steps. Neurotoxicity was evaluated using a wide range of quantitative morphological and behavioral readouts. AChE activity was measured using an Ellman assay. The toxicological profiles of the 7 OPs differed across the OPs and between adult and regenerating planarians. Toxicological profiles were not correlated with levels of AChE inhibition. Twenty-two "mechanistic control compounds" known to target pathways suggested in the literature to be affected by OPs (cholinergic neurotransmission, serotonin neurotransmission, endocannabinoid system, cytoskeleton, adenyl cyclase and oxidative stress) and 2 negative controls were also screened. When compared with the mechanistic control compounds, the phenotypic profiles of the different OPs separated into distinct clusters. The phenotypic profiles of adult vs regenerating planarians exposed to the OPs clustered differently, suggesting some developmental-specific mechanisms. These results further support findings in other systems that OPs cause different adverse outcomes in the (developing) brain and build the foundation for future comparative studies focused on delineating the mechanisms of OP neurotoxicity in planarians.

The ubiquitously occurring food contaminants alternariol monomethyl ether (AME), tenuazonic acid (TeA) and altertoxin II (ATX-II) are recognized as emerging Alternaria mycotoxins, yet substantial data gaps remain regarding their toxicokinetic characteristics. The hepatic metabolism of these three substances was investigated in primary rat (PRH) and human (PHH) hepatocytes by monitoring parent compound depletion and, where applicable, metabolite formation. AME was initially evaluated at 5 {micro}M and subsequently investigated over a concentration range of 0.75-8 {micro}M (0.75, 1.5, 3, and 8 {micro}M), whereas TeA was assessed at 5 {micro}M, and ATX-II was assessed at 0.22 and 1.11 {micro}M, with additional short-term experiments conducted over 30 min for AME and ATX-II, and over 10 min for concentration-dependent AME depletion. For AME, time-dependent clearance was further evaluated in PRHs at two hepatocyte densities, 0.25 and 0.5 million cells/mL. In PRHs, AME metabolism followed Michaelis-Menten kinetics (Vmax = 150.9 pmol{middle dot}min-{superscript 1}{middle dot}10- cells, Km = 1.18 {micro}M), whereas no reliable kinetic model could be established for PHHs. In contrast, TeA exhibited high metabolic stability, with only 9-10% depletion after 4 h, indicating negligible hepatic clearance in both species. ATX-II was also rapidly depleted and became undetectable within 30 min, accompanied by transient formation of altertoxin I (ATX-I), which was more pronounced in PHHs than in PRHs. Substrate depletion revealed pronounced interspecies differences in hepatic clearance capacity and stability. Overall, these findings provide comparative insights in primary human and rat hepatocyte systems, offering a foundation for future studies on their toxicological relevance and impact on human health.